Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

KIDNEYS AND URETERS

Figure 10.8. Primary renal hydatid disease. Unenhanced CT reveals a hypodense tumor in the left kidney. Peripheral daughter cysts and calcifications are evident. (Source: Polat P, Kantarci M, Alper F, Suma S, Koruyucu MB, Okur A. Hydatid disease from head to toe. RadioGraphics 2003;23:475–494, with permission from the Radiological Society of North America.)

Percutaneous needle aspiration tends to be nondiagnostic. Some patients require several explorations and numerous intraoperative biopsies to establish a correct diagnosis.

Similar to other sites, renal actinomycosis often progresses to extensive fistulas, including renoenteric fistulas. This chronic infection is a cause of retroperitoneal fibrosis and obstructive uropathy.

Botryomycosis

Botryomycosis, or a chronic bacterial infection consisting histologically of abscesses containing bacteria-bearing granules, is rare in the kidney. Most often Staphylococcus aureus is involved. The imaging appearance in some patients mimics a renal cell carcinoma. The diagnosis consists of detecting aggregates of organisms in sulfur-like granules within an abscess or urine. These granules should not be confused with actinomycosis.

Extensive cyst wall calcifications are common. A typical appearance is a calcified tumor compressing the pelvicalyceal system or ureter, at times identified even with conventional radiography. Similar to the liver, some cysts contain mural nodules (Fig. 10.8). The presence of a solid component within a cyst mimics a renal cell carcinoma. At times “sand” is detected in the dependent portion of a cyst. Daughter cysts lead to a multiloculated appearance. In time, calcified daughter cysts result in a cysts-within-a-cyst appearance, a finding suggesting the diagnosis.

Most hydatid cysts have mixed echogenicity on US.

As in the liver, percutaneous drainage of renal hydatid cysts is a therapeutic option.

Brucellosis

Brucellosis is rare in the kidney. These infections range from acute focal brucella nephritis, to a focal brucelloma, to diffuse. All ages are affected.

Actinomycosis

Renal actinomycosis is readily confused with a malignancy, leading to a nephrectomy.

Leishmaniasis

Infestation with protozoan parasites of the genus Leishmania ranges from cutaneous lesions to fatal systemic involvement. In southern France, Leishmania infantum is endemic, is carried by sand flies, and causes infantile leishmaniasis (Mediterranean visceral leishmaniasis).

Leishmaniasis of the genitourinary tract is rare. Its imaging appearance mimics pyonephrosis caused by more common organisms.

Filariasis

Chyluria, or white urine, is a complication of filarial infection, found most often in tropical regions. It is probably due to focal lymphatic rupture into collecting systems. In temperate climates chyluria is due to retroperitoneal malignancy, trauma, or chronic infection resulting in lymphatic obstruction.

Pedal lymphoscintigraphy using Tc-99m– sulfur colloid detects retrograde lymph flow into the kidneys.

Chyluria due to filariasis was successfully treated by endoscopic coagulation of suspected rupture sites, most often in a caliceal fornix (34).

Viral Infection

Hantavirus infection leads to an interstitial hemorrhagic nephritis, occasionally progressing to acute tubular necrosis (discussed in a later section). Some evidence suggests that Hantavirus infection is a risk factor for subsequent renal hypertension.

ADVANCED IMAGING OF THE ABDOMEN

Problems arise in detecting progression of renal damage. Neither IV urography nor US nor scintigraphy provides an accurate quantitative assessment of residual normal renal tissue. Computed tomography and probably MR can measure remaining renal parenchymal volume and thus provide prognostic data.

Chronic Pyelonephritis (Nephropathy)

Chronic pyelonephritis is not a single disease but rather a convenient description of a number of related entities. Pathologists tend to subdivide chronic pyelonephritis into interstitial and granulomatous varieties, with the latter including such entities as xanthogranulomatous pyelonephritis, malacoplakia, and renal tuberculosis.

An association between vesicoureteral reflux, urinary tract infection, and subsequent renal damage is well known, with such terms as reflux nephropathy and postinfectious nephropathy applied to this condition. If unchecked, renal injury has the potential to progress to overt endstage renal failure.

Vesicoureteral reflux in children progressing to intrarenal reflux leads to renal damage (intrarenal reflux implies reflux into ducts of Bellini). Reflux into collecting tubules is more common in compound papillae, which in turn are more often located in the renal poles. Thus intrarenal reflux and clinical chronic pyelonephritis progress to loss of renal parenchyma, typically at the renal poles, manifesting with imaging as renal scarring. Scarring results in inhomogeneous contrast enhancement and is also detected with DMSA scintigraphy. With progression, scarring eventually evolves into small, lobulated kidneys, distorted and clubbed calyces, and renal cortical juxtapapillary scarring, findings that are readily detected, although whether a small kidney is secondary to chronic damage due to vesicoureteral reflux or whether it represents congenital renal hypoplasia cannot be ascertained.

With enough loss of renal function, a noninvolved contralateral kidney becomes hypertrophic. At times normal residual parenchyma in a focally diseased kidney also undergoes compensatory hypertrophy.

Xanthogranulomatous

Pyelonephritis

Xanthogranulomatous pyelonephritis is an atypical, chronic renal inflammation often progressing to parenchymal destruction. It ranges from focal, where it mimics a neoplasm, to diffuse, but bilateral involvement is uncommon. With some, fistulas develop into surrounding structures, including the colon (35). It can evolve into an adjoining abscess. The involved kidney enlarges and either functions poorly or is nonfunctioning. Women are more often affected; it occurs in children, where this diagnosis is often not considered. In fact, in children xanthogranulomatous pyelonephritis and resultant end-stage pyelonephritis are not uncommon causes for a nephrectomy.

Histology reveals an inflammatory infiltrate containing large lipid-filled macrophages (xanthoma cells), fibrosis, and fat necrosis if the perirenal fat is involved. An uncommon association is with an underlying malignancy.

A common clinical presentation is anemia, leukocytosis, and flank pain. A majority of patients have urinary obstruction due to nephrolithiasis, at times even a staghorn calculus. Urography and US reveal calculi, hydronephrosis, or a renal tumor, findings that are nonspecific. Computed tomography findings include renal enlargement, usually the presence of a calculus, scattered hypodense regions representing obstructed calyces and other fluidfilled cavities, and, at times, extrarenal phlegmon extension. Chemical-shift MR aids in detecting fat. The kidney does not function with diffuse involvement. Inflamed tissue surrounding a cavity often enhances with contrast. An occasional fistula develops, including a renocolic fistula.

A minority of patients present with a tumoral form mimicking renal carcinoma, with imaging often suggesting a neoplasm, and even producing a vena cava thrombus. A biopsy is often nec-

KIDNEYS AND URETERS

essary to establish a diagnosis. In general, many of these patients eventually undergo a nephrectomy. There can be, however, total renal recovery on antibiotic therapy alone.

Malacoplakia

Malacoplakia is an uncommon chronic inflammatory condition (chronic tubulointerstitial nephritis) characterized by round intraand extracellular inclusions known as Michaelis-Gutmann bodies. Histology reveals large, foamy, granular macrophages with eccentric nuclei and prominent nucleoli containing laminated inclusions. Macrophage dysfunction appears to be the underlying pathogenesis. Its relationship to xanthogranulomatous pyelonephritis remains conjecture.

Malacoplakia affects a number of organs, with the urinary tract being the most common site. It develops in debilitated and immunocompromised patients. Some patients have had renal transplants. It is more common in women. Ureteral involvement is less common than renal. Occasionally it develops bilaterally. Recurrent E. coli infection is often detected. Inflammation tends to spread to adjacent structures. Needle biopsy is often diagnostic.

Contrast CT identifies variable enhancement of a soft tissue or partly cystic tumor or multiple tumors. Calcifications are not a feature of this condition. Hydronephrosis develops with extensive ureteral involvement.

Gallium-67-citrate scintigraphy reveals renal uptake; serial Ga-67 scanning identifies decreased uptake or complete resolution after antibiotic therapy, and this test appears useful in establishing an end point to therapy.

When extensive, malacoplakia mimics a neoplasm, inflammation, or even ureteritis cystica. An occasional scenario is that imaging detects a ureteral tumor, a carcinoma is suspected,and a nephroureterectomy is performed; malacoplakia is diagnosed only on histologic examination of the resected specimen.

Erdheim-Chester Disease

Erdheim-Chester disease, an uncommon systemic histiocytosis, is discussed in more detail in Chapter 14.Although retroperitoneal involvement is common, perirenal complications are

unusual and often consist of ureteral obstruction. Because tissue manipulation tends to exaggerate fibrosis, surgery should be avoided in these patients and obstruction treated with an endoprosthesis, if possible.

One patient with long-standing extraperitoneal Erdheim-Chester disease developed renal arteries stenosis, bilateral ureteral stenosis, and an adhesive capsulitis (36).

Sjögren’s Syndrome

Renal involvement is subclinical in many Sjögren’s patients. Yet the reverse is also true; at times renal involvement, including severe hypokalemia, is the initial manifestation of Sjögren’s syndrome.When present, it most often manifests as a tubulointerstitial nephritis or renal tubular acidosis and stone disease, including nephrolithiasis and nephrocalcinosis.

An inflammatory tumor develops occasionally. These tumors tend to be heterogeneous and hypodense with CT and hyperechoic with US. Differential diagnosis for such a tumor includes infection, infarction, and a malignancy.

Sinus Lipomatosis

At times a portion or almost the entire kidney is replaced by fat, most often unilaterally, called replacement lipomatosis. Rarely, perirenal or even periureteral tissues are also involved. Many of these patients have a long history of chronic infection, calculi, and renal atrophy. An obstructing calculus is identified in some, and these kidneys often have decreased function or are nonfunctioning. Xanthogranulomatous pyelonephritis, in particular, is often associated with lipomatosis, yet these are two distinct entities. Little evidence suggests a neoplastic association.

Histology reveals renal parenchymal atrophy and extensive replacement lipomatosis, in distinction to the large lipid-filled infiltrating macrophages found in xanthogranulomatous pyelonephritis

The involved kidney enlarges. Renal sinus fat is exaggerated and replaces atrophied parenchyma. This extensive fat deposition is identified by CT and US and aids in differentiating replacement lipomatosis from the infiltrative xanthogranulomatous pyelonephritis. At times the overall appearance suggests a fat-

containing neoplasm, but the latter generally results in little parenchymal atrophy.

Tumors

The Indeterminate Renal Tumor

Wide use of imaging techniques has led to a rise in the number of incidentally detected renal tumors. Although many are not associated with any clinical signs and symptoms and although most are shown to be simple renal cysts, a number are neoplastic and thus present a diagnostic dilemma. Imaging classification of some of these is straightforward, but others are indeterminate in their appearance. In particular, tumors <1cm in diameter are difficult to characterize by imaging, and the literature provides little guidance about their management. Initial annual imaging appears reasonable to establish whether growth occurs, but such an approach is based more on intuition than on any hard data. In the very young, the very old, and those with a limited life expectancy, an argument can be made for watchful waiting. Imaging and possible therapy of a small indeterminate renal tumor in a young adult poses a dilemma; if US is nondiagnostic for a simple cyst, an argument can be made for CT follow-up and resection only if it grows.

In general, CT and MR can readily distinguish between a benign cyst and a malignancy. More problematic is differentiating solid tumors—a renal cell adenoma, carcinoma, oncocytoma, metastasis, lymphoma, and other less common tumors tend to have a similar appearance. The differential diagnosis often also includes inflammatory conditions, some hemorrhagic or infected renal cysts, abscesses, and some vascular abnormalities. Imaging often cannot reliably distinguish between these conditions, with the exception of angiomyolipomas. A small but heterogeneous tumor generally represents a cancer, keeping in mind that CT shows some cancers to be homogeneous. At times CT suggests focal inflammation in a solid tumor by detecting peripheral rim contrast enhancement. Perinephric infiltration is found with both inflammatory conditions and lymphomas.

Most cancers tend to be hypoechoic on US; hyperechoic tumors range from angiomyolipomas, some cancers and an occasional adenoma.

ADVANCED IMAGING OF THE ABDOMEN

Hypervascular tumors are generally cancers but hypovascular tumors include cancers, adenomas, angiomyolipomas and even an occasional hemorrhagic cyst.

Phase-inversion tissue harmonic imaging is superior to B-mode US in study of focal kidney lesions (37); it achieves greater image quality, lesion conspicuity and better fluid-solid differentiation than B-mode US.

A renal tumor believed to contain a cystic component is best approached with US; many of these are identified as simple cysts. Complex cysts, however, are indeterminate with US and require further evaluation. Contrast CT, and lately MRI, are preferred for a tumor containing a solid component. If needed, scintigraphy using a cortical imaging agent distinguishes functioning renal tissue from nonfunctioning neoplasms. If the tumor is still indeterminate, biopsy provides a histopathologic diagnosis for most but not all solid tumors, although with current imaging few indeterminate renal tumors need a biopsy.

Among renal tumors suspicious for being malignant on CT, a majority appear heterogeneous on T2-weighted images and enhance on dynamic MRI. An occasional one does not enhance, primarily due to hemorrhage, but even these tend to be heterogeneous on T2-weighted images (38).

The role of 2-[18F]-fluoro-deoxy-D-glucose (FDG)-PET in evaluating indeterminate renal cysts is not defined, and currently insufficient evidence exists to suggest it for the study of indeterminate renal tumors.

Nonneoplastic

Ectopic Splenic Tissue

Ectopic splenic tissue within the kidney can mimic a solid tumor. A radionuclide spleen scan should suggest the diagnosis.

Lobar Dysmorphism

Renal lobar dysmorphism is a normal developmental variant that simulates a renal tumor. Some are detected incidentally by imaging. They range from intrarenal to peripelvic in location. Contrast CT can suggest the diagnosis; during the corticomedullary phase the oval-shaped lobar dysmorphism is detected in the perihilar